FIELD OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a method and an apparatus for detecting defects formed within a tire, and more particularly to a method and an apparatus for detecting internal defects formed within a pneumatic tire in a non-destructive manner.
Heretofore, there has been developed a technique for retreading or reforming a tire from a used tire. In case of manufacturing a retreaded tire, a used tire is first buffed to remove a worn tread and to form a substrate tire having a smooth outer surface and then a new tread is applied on the smooth outer surface. In order to obtain a retreaded tire having a good quality, the quality of the substrate tire is very important. For instance, if the substrate tire includes a defect such as a local separation, a circumferential separation and fatigue which are produced in the circumferential direction over 360 degrees, it is not possible to obtain a retreaded tire having a sufficiently high quality. Therefore, it has been earnestly required to develop a method of detecting the defect formed in the substrate tire for manufacturing the retreaded tire.
In Japanese Patent Application Laid-open Publication Kokai Sho 62-298744, there has been proposed a known method of detecting the defects in the tire. In this known method, a substrate tire for forming a retreaded tire is supported by means of two rollers and two pushers are urged against an inner surface of the tire at different forces. While the pushers are relatively moved in the circumferential direction of the tire to measure a difference in distortion or tension between the two pushers. Then the internal defect can be detected on the basis of the thus detected difference in distortion or tension.
In the known method just explained above, the pushers are urged against the inner wall of the tire, so that the difference in tension could not be detected accurately. That is to say, a number of reinforcing members are arranged near the inner surface of the tire, and therefore even if a separation is produced between these members, it is difficult to detect the tension difference at a high sensitivity. Further, the precision of the detection is very low. Moreover, in the substrate tire for manufacturing the retreaded tire, the separation is mainly produced at a third belt end on the outer side, but the known method is not effective for measuring such a defect.
Moreover, in the known method the pushers are moved relatively to the tire placed on the two rollers and the difference in distortion is detected. Therefore, the entire detecting apparatus is liable to be large in size. Further, it is rather difficult to hold the substrate tire stably on the two rollers, so that the operation becomes cumbersome and a large noise might be produced.
In the known method the difference in distortion between two points is detected, so that only the local separation can be detected and it is impossible to detect the circumferential separation generated along the entire circumference of the tire and the fatigue which has not been grown into the separation.